It is known to sometimes be necessary to reduce the coefficient of friction of a yarn in connection with processing it. A known method for doing this is the application of a paraffin wax. The traveling and sliding properties, in particular for machine-knitting and knitting, are considerably improved by the paraffin particles applied to the yarn. The application of paraffin takes place, for example, on bobbin winding machines during the rewinding of the yarn from cops to cheeses. In the process, the yarn is brought into contact with a paraffin body, which is used up by removal of the paraffin.
When a paraffin body is used up, or its contact with the yarn is interrupted, but not detected, the unwaxed yarn can cause yarn breaks during subsequent processing, or even needle breakage of a knitting machine, which leads to production errors or lost production. Therefore various methods and devices have already been proposed, which make possible monitoring of the paraffin application to the yarn.
Most methods are based on monitoring the paraffin body itself and signaling when it is detected that it has been exhausted. It is disadvantageous here that the contact of the paraffin body with the yarn can also be disrupted if the paraffin body is not exhausted, but is only jammed or dirty.
A method and a device are described in German Patent Publication DE 195 47 870 A1, by means of which the result of waxing can be checked. To this end, heat sensors are arranged in the path of the traveling yarn before and after the paraffin application device, which are charged with sliding friction by the traveling yarn. An increase in friction exceeding a defined value is interpreted as a defect in the paraffin application device, which results in switching of the respective bobbin.
Additional sensors are required for the known method and the known device, whose employment as a rule is not anticipated in a bobbin winding machine. It is therefore necessary to adapt the signal processing to these sensors.